B and T-lymphocytes, the effector arms of the immune system, traffic through the secondary lymphoid organs (lymph nodes, Peyers' patches, etc.) and peripheral tissues to sample the body for the presence of pathogens. B cells bind native proteins through specific cell surface receptors (BCR) for antigen presentation, whereas T cells (CD4+ and CD8+) rely on the remarkable ability of antigen presenting cells (APCs) to ferry antigens to their close proximity in the lymph node or spleen. This process of selective trafficking by cells of the immune system is critical to induce appropriate immune responses that would have the ability to impose immune containment of the pathogens. The strength of the primary immune response critically determines the level and duration of recall memory responses to the same antigen. The goal of vaccination is to induce immunological memory that persists for the life of the host. The DNA vaccine-induced expression of antigens is often inadequate to efficiently prime T cells. Under these conditions, a second signal in the form of co-stimulation involving cell surface proteins on APCs (B7 proteins, CD40) and T cells (CD28, CTLA4, and CD40L) is required for full activation of T cells. We tap into this particular ability of APCs to prime T cells, which would have the ability to efficiently induce HIV envelope-specific immune responses. HIV envelope is poorly immunogenic in various animal species (mice, macaques, and humans). One major reason being that the heavily glycosylated HIV envelope may not be easily accessible to the antigen presentation pathways of APCs. In the current proposal, we have devised a strategy in which HIV antigens could be targeted directly to APCs. The specific aims are: 1) Construction and expression of the envelope genes (gp120 and gp140) genetically linked to those coding for the T cell ligands, CTLA4 and CD40L. 2) Genetic immunization of mice with the gene fusion constructs and analysis of vaccine-induced immune responses (e.g., CTL assay, intracellular gamma INF production, tetramer stain, ELISPOT assay). 3) Testing of prospective candidate DNA vaccines for their ability to induce immune responses in rhesus macaques. Effective priming of T cells by both TCR engagement and targeted delivery of antigens via co-stimulatory molecules would have the potential to expand T cells that are critical for establishment and maintenance of immunological memory. The success of this novel vaccine approach will have major implications in the development of DNA vaccines having the ability to induce effective B and T cell responses in animals.